1. Field of the Invention
The present invention relates to the storage of digital data signals. More particularly, the invention concerns the storage and use of "managed" files, each comprising one or an aggregation of multiple constituent "user" files, in order to reduce file management overhead costs. Even more particularly, the invention involves the reclamation of wasted space that occurs within managed files due to deletion of some but not all constituent user files.
2. Description of the Related Art
The electronic management of data is central in this information era. Scientists and engineers have provided the necessary infrastructure for widespread public availability of an incredible volume of information. The internet is one chief example. In addition, the high-technology industry is continually achieving faster and more diverse methods for transmitting and receiving data. Some examples include satellite communications and the ever-increasing baud rates of commercially available computer modems.
With this information explosion, it is increasingly important for users to have some means for storing and conveniently managing their data. In this respect, the development of electronic data storage systems is more important than ever. And, engineers have squarely met the persistent challenge of customer demand by providing speedier and more reliable storage systems.
As an example, engineers at INTERNATIONAL BUSINESS MACHINES.RTM. (IBM.RTM.) have developed various flexible systems called "storage management servers", designed to store and manage data for remotely located clients. One particular system is called the ADSTAR.TM. Distributed Storage Manager (ADSM.TM.) product. With the ADSM product, a central server is coupled to multiple client platforms and one or more administrators. The server provides storage, backup, retrieval, and other management functions for the server's clients.
Although the ADSM product includes some significant advances and also enjoys significant commercial success today, IBM has continually sought to improve the performance and efficiency of this and other data storage systems. One area of particular focus is the time associated with storing a customer's file in a storage facility. Obviously, this time includes the actions of physically storing the data, known as input/output or "I/O" time. Additionally, file storage requires the expenditure of various "overhead" time, including (1) preparing the media to store the data ("media preparation overhead"), and (2) updating pointers, databases, tables, directories, catalogs, and other information maintained about the stored data ("bookkeeping overhead"). In the case of tape media, preparing the media for storage involves positioning the tape and advancing the tape to a desired speed. With disk media, preparation of the media requires time to spin-up the media, and also "seek time" to find a desired sector and track to begin writing.
The storage of each file requires both media preparation overhead and bookkeeping overhead, delaying completion of the entire storage process. The overhead for storage of a file is independent of that file's size. Thus, the overhead for a large file is overshadowed by its more substantial I/O time. The opposite is true with small files, where the necessary overhead dominates the file storage process compared to the file's relatively short I/O time. Consequently, I/O time is the chief obstacle in speedier storage or large files, whereas overhead prevents small files from being stored faster. Although some useful solutions have been proposed for these problems, IBM is nevertheless seeking better ways of addressing these problems to further improve the performance and the efficiency of its products to benefit its customers.